The present invention generally relates to grinding machines, and more particularly relates to the mounting of bearings used on grinding machine shafts.
Many different kinds of grinding machines are known in the prior art, including U.S. Pat. No. 4,997,135 to Zehr and U.S. Pat. No. 5,720,440 to Bonner, et al. Grinding machines include those machines that use a grinding means such as hammer mills, drum chippers, and wheel chippers to grind various materials. Grinding machines are used for grinding tree stumps and slash from logging operations; construction debris from damaged buildings, landfill garbage, tires for compacting purposes, and even apples for apple juice.
Generally and typically, these grinding machines utilize a grinding assembly attached to a frame to grind the material. One common type of grinding assembly is a hammermill assembly formed by a rotating shaft to which radially extending hammers are affixed. This hammermill shaft is mounted to bearing blocks and driven by a drive shaft which itself is interconnected by a clutch in some fashion to an engine assembly. The hammermill assembly is typically interfitted within a semi-circular hammermill screen. In use, material to be ground is dropped into a hopper from which it passes into the rotating hammers where it is broken apart and/or pulverized. The hammermill screen serves as a sieve, allowing ground material smaller than the pre-determined sieve holes of the hammermill screen to pass out of the hammermill assembly onto some sort of discharge system, conveyor, auger, or other device by which it is carried away. Material larger than the pre-determined sieve holes of the hammermill screen is kept in contact with the rotating hammers of the hammermill and reground until it is of a small enough size to pass through the sieve holes. In grinding machines for large materials, such as tree stumps or garbage, the shaft is typically quite large and heavy, and the heavy hammers create a very high rotating mass.
One major problem with such grinding machines occurs when certain materials (i.e., refrigerator compressors, manhole covers, engine blocks, rebar pieces, propane tanks, etc.) are fed into the grinding machine and when the grinding machine is over-loaded. The types or quantities of materials in the grinder can cause the parts of the grinding machine to stop rotating and cause damage to the grinding apparatus. For example, when the rotating hammers of a hammermill abruptly stop, the rotational energy must be transferred elsewhere. This energy is transferred to the shaft which then attempts to transfer the energy to the frame. When the shaft is solidly mounted to the frame and the frame will not absorb the energy, the energy is transferred back on to the shaft and the hammers, and back against the drive mechanism of the apparatus. As a result the grinding machine can literally tear itself apart, as the energy is turned back onto the machine itself causing damage to the parts of the grinding assembly, such as the hammers or grinding teeth, the grinding shaft, and grinding bearings, as well as damage to the drive mechanism. Other damage such as injury to persons and property in the vicinity of the grinding assembly can also occur. The cost from such sudden occurrences can be tremendous as repair and/or replacement costs are incurred as well as lost time, and productivity, to say nothing of the possible costs to lives and property that can be damaged.
What is needed is a method for dissipating the energy of such a sudden stoppage of rotation of the shaft, thereby alleviating damage to the grinding machine. What is also needed is a means for quick and easy replacement of parts if the grinding machine breaks. The present invention solves these needs.
The present invention is an improvement to grinding machines. Commonly, such a grinding machine will have a shaft and attached hammers for breaking apart large pieces of diverse material. This shaft will have first end extending to a second end, and is rotatable while attached to a frame through use of at least one pair of bearing assemblies. A first bearing assembly will support the first shaft end, and a second bearing assembly will support the second shaft end. The bearing assemblies are connected to a first shear plate having at least one hole that allows a shearing device to pass through. These shearing devices connect a first shear plate to the frame. The shearing devices are designed to have a lower resistance to a shearing force which is created when the rotation of the grinding device is jammed. When a jam occurs the shearing devices break. This releases the energy and prevents damage to other parts of the machinery.
In one embodiment of the present invention, the frame of the hammermill has a first plurality of shear bolt holes which are able to receive a first plurality of shear bolts. The frame further has a second plurality of shear bolt holes for receiving a second plurality of shear bolts. The first bearing assembly is able to attach to a first shear plate, and the second bearing assembly is able to attach to a second shear plate. Each of these shear plates have shear bolt holes which align with the shear bolt holes of the frame, so that the first shear plates"" shear bolt holes align with the frame""s first plurality of shear bolt holes. Thus, the first shear plate with attached first bearing assembly could be attached to the frame through use of shear bolts. Likewise, the second shear plate with attached second bearing assembly could be attached to the frame at the second plurality of shear bolt holes using the second plurality of shear bolts.
In use, if the grinding machine""s shaft becomes jammed or has other rotational difficulties, at least one or more of the shear bolts which bolt the shear plates to the frame will break, rather than the shaft or other components of the grinder or the bearing bolts holding the bearing assemblies to the plates (if present). By allowing the shear bolts to break, two advantages are shown. First, the damage caused by the jamming will be limited to replacement of the shear bolts which are designed to break at certain desired stress levels. Thus the potential damage to the remaining parts of the machine will be limited. Second, by allowing the shear bolts to break, the ability to fix the damage caused will be considerably easier. A user could simply dislodge whatever material had jammed the hammermill and then merely replace the broken shear bolt or bolts with a new shear bolt or bolts, refastening the bearing assemblies back into place.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by carrying out my invention. As will be realized, the invention is capable of modification in various obvious respects all without departing from the invention. Accordingly, the drawings and description of the preferred embodiment are to be regarded as illustrative in nature, and not as restrictive.